Preparation and electrochemical properties of N, S co-doped paper fiber carbon foam (PFCF) electrode materials for supercapacitors

Biomass fiber, as a renewable resource, can be used to prepare advanced materials for energy storage. Herein, a simple foaming technique, stirring the paper fiber in a surfactant solution, is used to produce porous materials with a foam structure. Then using KOH and K₂CO₃ as the double-activators to further form hierarchical pores, the paper fiber carbon foam (PFCF) materials are prepared. The pore size distribution, porosity and specific surface area of the materials can be regulated by changing the ratio of the two activators. This study shows that the optimal PFCF has excellent porous structure, with a specific surface area of 1693.74 m²·g⁻¹ and a pore volume of 1.529 cm³·g⁻¹. Furthermore, nitrogen and sulfur co-doped PFCF electrode material (N, S-PFCF) is prepared by the heteroatom doping. The prepared N, S-PFCF-750 has a specific capacitance of 245.24 F·g⁻¹ at a current density of 0.1 A·g⁻¹, and a capacity retention rate of 65.5% at higher current density (20 A·g⁻¹). Finally, the assembled symmetrical N, S-PFCF-750//N, S-PFCF-750 double-layer supercapacitor has an energy density of 13.24 Wh·kg⁻¹ at a power density of 500 W·kg⁻¹. At the current density of 20 A·g⁻¹, the capacity retention rate is 91% after 10,000 charge-discharge cycles, showing stable electrochemical reversibility and good capacity retention rate.